1. Field of the Invention
The present invention is related, in general, to an electrode patch and/or a wireless system for measuring the physiological condition of a subject, and more particularly to an electrode patch for ECG monitoring. The present invention further includes a method of sensing and analyzing a physiological signal.
2. Technical Background
Monitoring one or more physiological conditions of a patient is well known. Medical patient monitoring systems are highly sophisticated utilizing telemetry systems at a central receiving and monitoring station. ECG monitoring has the greatest applications.
According to present estimates, approximately 60 millions Americans have one or more types of cardiovascular disease including high blood pressure, coronary artery disease, stroke, rheumatic heart disease, congenital cardiovascular defects and congestive heart failure. Cardiovascular disease claims approximately one million lives in the United States each year, or approximately forty percent of all deaths. Since 1990, cardiovascular disease has been the number one killer in the United States every year other than 1918. More than 2,600 Americans die each day of cardiovascular disease, which is an average of 1 death every 33 seconds.
Because heart performance can deteriorate quickly, the key to effective cardiovascular disease management resides in early medical intervention. Patients often do not recognize subtle changes in cardiovascular disease symptoms and may not appreciate the importance of quickly reporting such changes to their physician. To make early intervention possible and prevent rehospitalization, healthcare providers need daily access to accurate information about patients' symptoms. There are many reasons a physician may want to monitor patients on a continuous or nearly continuous basis. These include the need to detect episodic arrhythmias, either to establish a diagnosis or to evaluate efficacy of therapy; the need to help evaluate syncope, in particular to detect any associated cardiac rhythm disorder or to assess therapy; the need to assess efficacy of therapy for atrial arrhythmias (this is especially important with atrial fibrillations in patients at risk for stroke or systemic embolism who can not take warfarin or similar drugs); the need in patients at increased risk for sudden arrhythmic death, particularly for example those patients with ventricular dysfunction who would benefit from prolonged (6 weeks to 6 months) ECG monitoring after serious events such as a myocardial infarction, an episode of cardiac decompensation, recent cardiac surgery or the onset of new therapy with an antiarrhythmic agent; and the need for providing patients with at home immediate access to 911 emergency help without patient action particularly for those patients who have had multiple myocardial infarctions.
A typical diagnostic process for any of these cardiovascular conditions may include one or more of the following tests: ECG; Holter monitor; external loop recorder; implantable loop recorder; tilt table test; electrophysiology study; and a stress test. An ECG can be performed in a physician's office or a hospital setting. It is unlikely, however, a patient will undergo many of the symptoms associated with these conditions such as for example syncope or fibrillation in those few minutes. A Holter monitor is a device that measures and records heart rhythm, usually over 1 day but occasionally for 2 or more days. Holter monitors can miss recording a critical moment when a diagnosis could be made because the event doesn't happen during the recording, or because the patient took the device off to sleep. This is particularly important where patients do not want to wear the device to work for fear of discrimination if their employer or fellow employees know they have a health problem. An external loop recorder is a device that monitors heart rhythm and rate for up to a month. During this test, the patient wears a device on the wrist, around the chest or in a pocket. The patient must press a button on the device to make a recording of the heart activity during the period the symptoms occur such as fainting. Unfortunately, this only occurs if the patient is sufficiently aware that the event took place. Furthermore, the information collected must be downloaded periodically making in more difficult for the patient to comply. Implantable loop recorders are relatively new devices. These devices suffer from these same drawbacks as well as the possibility of infection due to the invasive procedure used to implant the device. A tilt table test is used to simulate conditions that may cause fainting. It enables the physician to gauge how blood pressure, heart rate and rhythm respond to a change in position from lying down to standing. This test is expensive and is generally only done in a large or teaching hospital setting. An electrophysiology study is an expensive and invasive procedure. This procedure threads a catheter into the heart to record the heart's own electrical impulses and to assess the response to pacing and extra beats. Other tests such as cardiac stress tests are expensive and generally are performed in a hospital setting.
Traditional tests leave large numbers of patients with recurrent, unexplained, undiagnosed cardiac problems after undergoing these tests. The primary reasons these tests fall short are: 1) They only monitor the heart for a relatively limited amount of time, or 2) They require the patient to wear a device in their daily living that is embarrassing and inconvenient to wear, and/or that requires them to perform a task after experiencing a symptom. Therefore, there is a need for a diagnostic tool that allows one to continuously monitor the heart's rhythm and rate for long periods of time, on the order of several months or more, and requires no action by the patient at the time of fainting.
While a number of technologies have been developed to allow for patient monitoring at home or on the go, each of these technologies suffer from one or more major drawbacks. U.S. Pat. No. 5,458,124 to Stanko et al. describes an electrode and wireless transmitter system for use in measuring the physiological condition of a subject. The system in Stanko due to the rigidity of the system doesn't allow for good electrode contact with the patient's skin. Furthermore, the system in Stanko doesn't provide a good means for data error detection, nor in process adjustment by an external source. U.S. Pat. Nos. 5,862,803; 5,957,854; and 6,289,238 to Besson et al. provide for a wireless electrode system for measuring various body conditions. This system, however, is cumbersome, overly complex and limiting in that among other things it requires separate electronics for each electrode, as well as, a source of power external to the electrode. Because of the unique power requirements, this system presumably doesn't allow for remote wireless monitoring at any great distance thereby creating an invisible tether to the receiver and limiting the versatility of the system.
The wireless technologies outlined above are interesting, but are not applicable for the easy measurement physiological signals and transmission over long periods of time. A compact, wireless physiological monitoring technology is needed for this purpose. It is therefore, an object of this invention to provide an electrode patch and wireless system for such a purpose. It is a further object of this invention to provide an electrode patch and wireless system with a feasible battery system. It is still a further object of this invention to provide an electrode patch and wireless system that allows for good measurement from two or more electrodes. It is still further an object of this invention to provide an electrode patch and wireless system that provided for data error correction. It is still further an object of this invention to provide an electrode patch and wireless system, which utilizes dry physiological electrodes for detecting the physiological signals.